Dynamic port for measuring reactor coolant pump bearing oil level

ABSTRACT

A dynamic port that extends from the bottom wall of an oil reservoir that surrounds the lower guide bearing of a reactor coolant pump and is in fluid communication within an oil level gauge. The dynamic port is rotatable into and out of the oil flow path to adjust the dynamic oil level shown by the oil level gauge when the pump is at operating speed to be substantially equal to the static oil level when the motor is at rest.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No.12/493,261, filed Jun. 29, 2009, entitled “Dynamic Port for MeasuringReactor Coolant Pump Bearing Oil Level.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus for measuring the level in anoil reservoir of a motor and more particularly to such apparatus formeasuring the dynamic oil level in a reservoir surrounding a bearing ona motor shaft. More particularly, the invention relates to apparatus formonitoring the level of lubricating oil in the oil pot of a motor, theinvention having particular application to reactor coolant pump motorsin nuclear power plants.

2. Description of Related Art

The reactor coolant pump motors drive the reactor coolant pumps whichare part of the primary reactor coolant system in a nuclear power plant.The motors are typically arranged with vertical shafts. The bearing andlubrication system of a vertical motor is usually contained in twoseparate oil pots (also referred to as oil reservoirs). An upper oil potcontains the upper guide or radial bearings and the total thrust bearingsystem. The lower oil pot contains the lower guide or radial bearings.Each of these oil pots is typically provided with cooling coils forcarrying cooling water to dissipate the heat which is generated by thebearing systems.

The design of the oil pots is such that the oil level within the potshould be monitored during operation to ensure that the oil level is notrising above or falling below the expected levels. A rising level mightindicate, for example, a water leak within the cooling coils whichresults in water entering the pot and mixing with the oil. If such asituation were to persist, the lubricating ability of the oil would besharply diminished and, more importantly, the oil/water mixture wouldoverflow the pot and migrate toward the hot reactor coolant pump, wherea fire could result.

A falling oil level would be indicative of a leak in the oil pot systemwhich allows oil to escape from the pots. If this situation persists,the level of oil in the pot would drop below the level where the oillubricates the bearings and thus result in severe damage to the bearingsand possibly to the motor shaft/runner. More importantly, this conditioncould also result in a fire if the oil, with a flash point of 420degrees fahrenheit (215.56 degrees centigrade) reaches the pump surfaceswhich may be as hot as 550 degrees fahrenheit (287.87 degreescentigrade).

Because of these real and serious concerns, each of the two oil pots isequipped with an oil level detector which provides an alarm signal to acontrol room in the event of an unusual oil level condition. Someconcern exists that the detector may generate a high level alarm when,in fact, the system is operating normally, i.e., there is no leakage ofwater into the oil pump. A major contributor to this potential problem,particularly with respect to the lower oil pot, is the expansion of theoil due to heat entering the oil pot from the reactor cooling pump. Atemperature rise of 50 degrees fahrenheit (10 degrees centigrade) in theoil of the oil pot, for example, would result in a volume expansion ofapproximately 0.6 gallon (2.27 liters) in a 30 gallon (113.56 liters)capacity pot. This is reflected in the rise of the oil level within thepot and the detector of 0.5 inch (1.27 centimeters) or more, and couldresult in a spurious high level alarm signal.

Recently, a number of nuclear plant operators of pressurized waterreactors have experienced a high oil level alarm on the lower bearingoil reservoir shortly after reaching normal operating temperature andpressure. The oil level during the start-up period had graduallyincreased during heat-up from an initial level of +0.8 inches (+2.0centimeters) immediately following the across-the-line start. One plantoperator noted that upon initial start-up of the pump motor, the oillevel abruptly increased from the static zero level to this initialdynamic level. In the attempt to clear the ensuing alarm, two actionswere performed. First, the lower oil level alarm switch assembly wasadjusted approximately 3/16 of an inch (0.48 centimeters) upward, to themaximum limit of adjustment. This raised the alarm actuation for boththe high oil level alarm point as well as the low oil level alarm pointfor the lower bearing oil reservoir. Prior to this adjustment, the loweroil reservoir alarms were set to occur at approximately +1.25 inches(+3.2 centimeters) above static for the upper alarm and approximately−1.25 inches (−3.2 centimeters) below static for the lower alarm.Second, the vent line between the oil level sight glass and the oilalarm reservoir was disconnected right above the sight glass ventingboth the alarm reservoir and the sight glass to the containmentatmosphere. These directions were taken to clear the oil level alarmencountered during the heat-up of the plant by raising the overall alarmwindow and provide a more representative oil level based on a known oilinventory in the lower oil pot.

As the plant heat-up continued, the lower oil reservoir againexperienced a high level alarm at 1.3 inches (3.3 centimeters) above thestatic oil level. The plant went on to operate at power and continued toexperience a high oil level alarm; with the oil level oscillatingbetween +1.3 and +1.5 inches (+3.3 and +3.8 centimeters) and trackingwith changes in ambient and component cooling water temperatures.

The main purpose of the oil level indicating system on the main coolantpumps in pressurized water reactor systems manufactured by WestinghouseElectric Company LLC is for monitoring the oil inventory within thebearing oil reservoir. The original design concept behind the systemused on the lower guide bearing oil reservoir on Westinghouse reactorcoolant pump motors was a simple transference of indicated oil levelfrom inside the bearing oil reservoir to an alarm switch reservoir andsight glass which is external to the lower bearing oil reservoir(sometimes referred to herein as the oil pot). This approach was takento eliminate errors due to turbulent flows within the bearing oilreservoir that would be generated if the alarm float switch and sightglass were placed directly into the bearing oil reservoir.

The technical principle for the design of the oil level indicatingsystem of Westinghouse reactor coolant pump motors is a simple forcebalance accomplished by transference of the pressures from the bearingreservoir to the alarm reservoir generated by the static elevation of acolumn of fluid. When the fluid is at rest, the height and thereforepressure differences of the oil columns in each reservoir are equal,assuming homogeneous temperatures and fluid properties throughout thesystem. The alarm reservoir oil level therefore matches the bearingreservoir oil level and oil inventory is easily monitored. Once thefluid is set in motion, however, it's been observed that the pressuresin the bearing reservoir can change due to variations in temperature andvelocity of the oil. This may unbalance the forces acting on the two oilcolumns causing unequal heights, or levels, of the columns The oil mayalso become mixed with air, i.e., aeration; causing changes in oilproperties that can tend to contribute to changes in the height of oneor both oil columns. Thus, an oil level indicating system must considerthese factors in addition to those of the operating environment whenused for oil inventory monitoring.

SUMMARY OF THE INVENTION

It is in general logic of this invention to provide an improved oilreservoir arrangement for a vertical shaft pump motor which avoids thedisadvantages of prior arrangements while affording additionaloperational advantages.

An important object of this invention is the provision of oil levelmonitoring apparatus for a pump motor oil reservoir which minimizes thedynamic affects of thermal expansion and hydraulic forces acting uponthe oil.

In connection with the foregoing object, it is another object of thisinvention to provide an oil level monitoring apparatus which is simpleto use and can be adjusted to accommodate for the unique characteristicsof each plant.

It is another object of this invention to provide an oil levelmonitoring apparatus of the type set forth which minimizes the chance ofspurious high level alarm signals.

In connection with the foregoing objects, it is another object of thisinvention to provide an oil level monitoring apparatus of the type setforth which is of simple and economical construction and contains nomoving parts and consumes no power.

These and other objects of the invention are attained by providingapparatus for monitoring the level of bearing lubricating oil in the oilreservoir of a nuclear reactor coolant pump motor which has apredetermined normal oil level, the apparatus in part comprising: avertical shaft; a bearing supporting the shaft; an oil reservoir forretaining a body of oil in fluid communication with the bearing; anindicator for indicating an oil level in the reservoir; and a fluid portextending into the reservoir and operatively connected with theindicator, the orientation of the fluid port within the reservoir beingadjustable to compensate for the dynamic affects on the body of oilresulting from rotation of the rotatable shaft—the dynamic affectsincluding such factors as thermal expansion of the oil and hydraulicforces.

In one preferred embodiment, the fluid port includes a hook shaped or an“L” shaped tube that extends vertically into the body of oil with aperipheral end bent horizontally and in fluid communication with theoil. Preferably, the vertical portion of the generally “L” or hookshaped tube is sealed to a bottom of the reservoir with a compressionfitting. Desirably, the fluid port is adjustable by being rotatableabout an axis of the compression fitting and vertical section of thetube.

Additionally, the foregoing objectives are achieved by a method ofdetermining an oil level in such an oil reservoir including the stepsof: determining the level of oil in the reservoir as indicated by theindicator when the motor is substantially in a static condition;bringing the motor up to an operating speed; and adjusting the fluidport within the reservoir until the indicator indicates substantiallythe same oil level at operating speed as it did in the substantiallystatic condition. Preferably, the adjusting step is carried out shortlyafter the motor reaches operating speed and temperature and isaccomplished by rotating the fluid port about an axis of a verticalsection of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the invention can begin from the followingdescription of the preferred embodiments when read in conjunction withthe accompanying drawings in which:

FIG. 1 is the fragmentary elevational view, in partial section, of areactor coolant pump motor incorporating the oil level indicating systemof the prior art;

FIG. 2 is the enlarged fragmentary view in vertical section of the lowerportion of the pump motor of FIG. 1 showing an enlarged view of the oillevel indicating system of the prior art;

FIG. 3 is a diagrammatic view of a lower oil reservoir of a prior artreactor coolant pump motor, with the oil therein at a normal level;

FIG. 4 is a perspective view of the lower guide bearing oil reservoir ofthis invention with a portion thereof cut away to show the “L” shapedfluid inlet port to the oil level indicating system of this invention;and

FIG. 5 is a perspective view of the lower guide bearing oil reservoir ofthis invention with a portion thereof cut away to show the hook shapedfluid inlet port to the oil level indicating system of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, there is illustrated a reactorcoolant pump motor, generally designated by the numeral 10, which is ofconventional construction. The motor 10 includes a vertical shaft 11 onwhich is mounted a rotor core assembly (not shown) surrounded by astator core assembly 13 which is supported between lower and upperbrackets 14 and 15. The upper end of the shaft 11 carries a flywheel 16mounted within a flywheel cover 17. The shaft 11 is provided with upperand lower annular runners 18 and 19.

The upper runner 18 extends into an annular upper oil pot 20 encirclingthe shaft 11 and is disposed for engagement with an up-thrust bearing22, and down-thrust bearing 23 and an upper guide bearing 24, alldisposed within the upper oil pot 20. The lower runner 19 extendsdownwardly into an annular lower oil pot 30 which encircles the shaft 11and is supported on a plurality of equiangularly spaced-apart lowersupport webs 25, the webs 25 being interconnected by an annular supportplate 26 and by cylindrical connecting webs 27.

Referring to FIGS. 1 and 3 of the drawings, the lower oil pot 30includes a cylindrical outer wall 31 and a cylindrical inner wall 32,the walls 31 and 32 being interconnected by an annular bottom wall 33.Fixedly secured to the outer wall 31 at the upper edge thereof is acircular head rail 34 which supports thereon an annular seal 35, agasket 36 being provided therebetween. The seal 35 is disposed insealing engagement with the runner 19 of the shaft 11. Carried by thehead rail 34 within the oil pot 30 is a support ring 37 (FIG. 2). Aplurality of bearing shoes 38 are disposed for bearing engagement withthe outer surface of the runner 19 at equiangularly spaced-apart pointstherearound, the bearing shoes 38 being respectively held in engagementwith the runner 19 by a plurality of adjusting screws 39 carried by thesupport ring 37.

All of the structure described above is of a conventional constructionand is provided in prior art reactor coolant pump motors. The lower oilpot for such a prior art motor is disclosed in a front elevational viewpartially in section in FIG. 2 and diagrammatically in FIG. 3. The oilpot 30 contains a volume of oil 40 which, at ambient temperatures,normally fills the oil pot 30 to a level 41 illustrated in FIG. 3. Aplurality of cooling coils 42 carry cooling water through the oil pot 30for cooling the oil 40 therein. The oil pot 30 communicates at a port 43in the bottom wall 33 with a conduit 44 which connects through a valve45 to one or more oil level gauges, which may include a float gauge 47and the sight gauge 49. Both of the gauges 47 and 49 are in liquidcommunication with the conduit 44 so that the oil rises therein to thesame level 41 as is present in the oil pot 30. The float gauge 47carries a floating element which is disposed for magnetically operatinghigh and low sensor switches to indicate abnormally high and low levelsof the oil 40 in the oil pot 30. The sight gauge 49 typically includes atransparent window portion so that the level of oil 40 therein can bevisibly observed.

The high level indication is to indicate excess fluid in the oil pot 30which might be occasioned by a water leak within the cooling coils 42,resulting in water entering the oil pot 30 and mixing with the oil 40.Such a high level would typically trigger an alarm signal, since thedilution of the oil 40 would lessen its lubricating ability and, moreimportantly, as the leak continued the oil/water mixture might overflowthe oil pot 30 and contact the hot reactor coolant pump causing a fire.The low level sensor is for the purpose of indicating a falling oillevel in the oil pot 30, which might be indicative of an oil leak. Sucha low level would trigger an alarm signal since a continued leak wouldcause the oil level to drop to the point where the oil no longerlubricates the bearing shoes 38, resulting in severe damage to thebearing shoes and, possibly to the motor shaft 11 and/or runner 19.Furthermore, this condition could also result in a fire if the leakingoil were to contact the hot pump surfaces.

In this prior art arrangement, the oil 40 in the oil pot 30 tends toexpand when heated. Indeed, despite the cooling effect of the coolingcoils 42, the oil 40 may be heated to such an extent that it expands toa level such that it will actuate the high level sensor in the floatgauge 47 setting off a high level alarm. Such an alarm is spurious sinceit is not occasioned by excess fluid in the oil pot 30.

If one accepts that the lower guide bearing reservoir 30, when filled tothe normal static level has the proper inventory of oil in which tooperate, and any change to the observed level within the alarm assemblyfollowing motor start-up is due to factors acting on this properinventory, then we can also accept that the dynamic oil level will reachan equilibrium that also represents the proper inventory of oil.

The factors that influence the observed dynamic, or running, oil levelare primarily hydraulic and thermal. These factors have a direct andpredictable outcome in the change of observed oil levels between staticand dynamic conditions. As the motor accelerates to speed, the velocityof oil within the lower bearing oil reservoir 30 increases, as doesturbulence within the reservoir. In addition, temperature changes fromthe production of heat due to the rubbing velocity of the bearing 38 andthe journal (shaft) 11, as well as increases in containment temperaturemay affect the overall volume but not the inventory of oil. Temperaturechanges cause changes in density and viscosity of the oil, resulting inthermal volumetric expansion and changes in oil flow velocities.Additionally, some amount of oil aeration is expected to occur due tothe turbulence and splashing of the oil, causing further volumetricexpansion of the oil in the system. When thermal and hydraulicconditions stabilize, the dynamic oil level stabilizes and becomes a newbaseline reference oil level that is the proper dynamic indication ofoil inventory.

Depending on the lower bearing assembly and oil level indicating systemdesigns, the baseline reference level may, in fact, match the staticlevel, but this ideal performance is not always achieved, as the dynamiclevel often deviates from the static level. This deviation usually isunimportant. What is important is that the level obtained with the motorenergized at normal operating temperature and pressure remains stablewithin a tolerance band once thermal and hydraulic equilibrium isachieved. Fluctuations due to normal variations in ambient and coolingwater temperature are expected and acceptable. The baseline referencelevel can also vary between different motors depending on the particulardesigns of the lower guide bearing, the oil reservoir, and the levelindicating system, and also due to variations in operating conditions,particularly thermal variations. This too is acceptable and expected.Variations in oil level and other motor parameters also have beenobserved to occur when one motor is moved to another motor compartmentin the same power plant. The difficulty with the current oil levelsystem is that the oil level alarm switch assembly on this motor doesnot have sufficient adjustment range to place the high alarm above thebaseline reference level to prevent alarm actuation. Thus, the baselinereference level exceeds the high alarm level causing an alarm conditionwith the plant at power, which is not acceptable.

As illustrated in FIG. 4, this invention provides a new dynamic port 50in the bottom wall 33 of the oil reservoir 30 that seats in the existingport 43 that is in fluid communication with the gauge conduit 44. Thepurpose of the dynamic port 50 is to allow for the ability to adjust, ortune, the observed running oil level at the lower oil reservoir inreactor cooling pump motors, back to the static level, which willprevent unwarranted level alarms and misunderstandings about actual oilinventory. The dynamic port 50 provides a means to adjust the oilpressure transmitted to the alarm reservoir and sight glass measurement,allowing utility operators to have a consistent and reliable oil levelreading during operation. As lubrication and heat removal is such acrucial element of bearing life, the inaccuracy of the currentmonitoring system is unacceptable and this modification will cure thatproblem for utility operators.

One preferred embodiment of the dynamic port 50 illustrated in FIG. 4comprises a generally “L” shaped tube having an approximately straightvertically extending section 51 which extends from the port 43 upwardsand bends horizontally to form the peripheral section 52 that has anopening at its distal end that is in fluid communication with the gaugeconduit 44 through the port 43 in the bottom wall 33 of the oilreservoir 30. A compression fitting 53 functions as the primary seal inthe bottom wall 33 of the oil reservoir 30 and also forms the means ofadjustment to turn the port 50 so that the horizontal section 52 canrotate about its vertical section 51 to adjust the dynamic oil level inthe level indicating gauges 47 and 49. When the motor is running duringpower plant start-up, the dynamic port 50 may be positioned as neededinto or out of the flow path of the oil in order to transmit a pressureto the float guide alarm reservoir 47 and sight gauge 49 that will bringthe running oil level back to the static oil level. Thus, the method ofthis invention determines the level of oil in the reservoir as indicatedby the oil level indicators 47 and 49 when the motor is in asubstantially static condition, i.e., not running When the motor isbrought up to normal operating speed and temperature, the dynamic port50 is adjusted by rotating the port until the oil level indicatorindicates the same oil level at operating speed as it did in thesubstantially static condition. Though the dynamic port 50 is shown ashaving an abrupt right angle between the vertical section 51 and thehorizontal peripheral section 52 it should be appreciated that thetransition between the two sections 51 and 52 can be gradual, in theincrements or rounded.

FIG. 5 illustrates another preferred embodiment of the dynamic port 50.Like reference characters are used for the components of FIG. 5 thatcorrespond to the components of FIG. 4. The only difference in FIG. 5over that shown in FIG. 4 is that the dynamic port 50 has a hook shapewhich increases its sensitivity. In addition, the hook shape enables thedynamic port to be inserted through the existing opening 43 in the floor33 of the oil pot 30. In all other respects the embodiment shown in FIG.5 operates the same as was described for the embodiment illustrated inFIG. 4.

Therefore, while a generally hooked shaped and “L” shaped dynamic port50 have been illustrated, it should be appreciated that the shape of thedynamic port can be any shape with a vertical component that protrudesthrough the floor of the oil pot via a seal, where the tip can bemanipulated to adjust the pressure. For example, the dynamic port 50 mayhave a flexible tip that can be reshaped to accomplish the objective oflowering the dynamic oil level reading.

Accordingly, while specific embodiments of the invention have beendescribed in detail, it will be appreciated by those skilled in the artthat various modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular embodiments disclosed are meant to beillustrative only and not limiting as to the scope of the invention,which is to be given the full breadth of the appended claims and any andall equivalents thereof.

1. A nuclear reactor coolant pump motor, comprising: a rotatable shaft;a bearing supporting the shaft; an oil reservoir for retaining a body ofoil in fluid communication with the bearing; an indicator for indicatingan oil level in the reservoir; a fluid port, a portion of the fluid portextending into and above a bottom of the reservoir, the fluid portoperatively connected with the indicator, the orientation of the portionof the fluid port extending into and above a bottom of the reservoirbeing adjustable to compensate for the dynamic affects on the body ofoil resulting from rotation of the rotatable shaft.
 2. The nuclearreactor coolant pump motor of claim 1 wherein the fluid port is a tubehaving a vertical section that extends through and above the bottom ofthe reservoir and is sealed to a floor of the reservoir.
 3. The nuclearreactor coolant pump motor of claim 2 wherein the fluid port includes an“L” shaped tube that extends vertically into the body of oil with aperipheral end bent substantially horizontally and in fluidcommunication with the oil.
 4. The nuclear reactor coolant pump motor ofclaim 2 wherein the fluid port includes a hook shaped tube that extendsvertically into the body of oil with a peripheral end bent substantiallyhorizontally and in fluid communication with the oil.
 5. The nuclearreactor coolant pump motor of claim 2 wherein the vertical portion ofthe tube is sealed to the bottom of the reservoir with a compressionfitting.
 6. The nuclear reactor coolant pump motor of claim 2 whereinthe fluid port is adjustable by being rotatable about an axis of thevertical section of the tube.